1. Field of the Invention
This invention relates to a method and apparatus for managing print jobs in a print shop system for printing documents that contain both color and black and white pages. In particular, it relates to an improved method for detecting color components in such documents for purposes of assigning documents to appropriate printers for printing.
2. Description of Related Art
A professional print shop typically has a plurality of printers connected to a server by a network, where the server controls the printing of customer jobs on one or more printers. The printers in a print shop typically have different characteristics and capabilities. In particular, a print shop typically has both black and white printers and color printers. A conventional practice is to print documents containing only black and white (B&W) pages using black and white printers, and to print documents containing B&W as well as color pages using color printers. Here, the term B&W page includes a page with gray-level images, which can be printed on a B&W printer using black ink or toner, for example, as halftone images. Printing with a color printer is typically more costly than printing with a black and white printer.
An improved print shop management method allows a document containing B&W as well as color pages to be split into two sub-documents, one color document and one B&W document, and prints the two documents using two separate printers, one color printer and one B&W printer, respectively. In a method described in commonly owned U.S. Pat. Appl. Pub. No. 2007/0229881A1, when a document to be printed contains both color and B&W pages, the server splits the print job into a color and a B&W sub-job. Each print job includes a job ticket containing a plurality of parameters and the document to be printed. The server splits the original print job by generating a color sub-document and a B&W sub-document based the color characteristics of the pages of the original document, and generating a color sub-job ticket and a B&W sub-job ticket based on the original job-ticket parameters, by suitably retaining some original parameters, overriding some, deleting some, retaining some with page shifting, and adding some parameters. The two sub-jobs are printed by two different printers and the printed pages are then merged into one set of pages. In another method described in commonly owned U.S. Pat. Appl. Pub. No. 2008/0079963A1, to print a document having both color and B&W pages using N-up and/or duplex printing, the server determines whether to print the entire document on a color printer or to split the document into two sub-jobs and print them on a color printer and a B&W printer, respectively.
In order to determine how to assign a print job to appropriate printers, the server needs to determine whether each page of the document is a B&W page (i.e. it contains only black and white content) or whether it is a color page (i.e. it contains color content, whether or not it also contains B&W content).